This invention relates to a control that utilizes the absorption solution temperature as feedback for controlling the amount of heat delivered into an absorption chiller at start-up.
Absorption solution/refrigerant systems are utilized in many applications to provide chilled or heated water for environmental control in buildings, etc. In a basic system, an absorber separately receives a flow of an absorption solution (concentrated LiBr), and a refrigerant. The refrigerant is often water. The refrigerant is directed onto a tube, which would carry water to be chilled for part of a building air conditioning system. The absorption solution is also directed into the absorber and is cooled. Within the absorber, the absorption solution and the liquid refrigerant combine. The absorption solution, at this point, is at the proper temperature and concentration that enables it to absorb the refrigerant vapor. It will then carry this refrigerant with it as it is returned to a generator.
In the generator, a heat source is applied to the mixed absorption solution and refrigerant, which boils off a portion of the refrigerant. This warmer refrigerant vapor is passed through a condenser where it is cooled and changed into liquid refrigerant. The liquid refrigerant is then sent to the evaporator where it cools the tubes carrying water for building air conditioning. The refrigerant evaporates and changes into vapor. This vapor is allowed to flow into the absorber unit. Here the water vapor is absorbed into the absorption solution being returned from the generator
Notably, an absorption chiller is utilized to provide chilled water for use in an air conditioning system. The same system can be utilized to provide heated water, with some rearrangement of flow, etc. For purposes of this application, the invention extends to both heating and cooling systems utilizing an absorption solution. While the application describes an “absorption chiller,” the invention extends to absorption solution/refrigerant systems that can be utilized to either chill or heat water. A worker of ordinary skill in the art would recognize how the disclosed system would be modified to function as an absorption heater.
At start-up, it would be desirable not to immediately subject the generator to the full heat of the system under some conditions. If the heat is directed into the chiller immediately, there is undesirable vibration, and noise, due to vapor being mixed with solution in the heat exchanger pipes, and rapid thermal expansion. These effects can reduce product life and also cause undesirable noise. The example above is for startup conditions but those skilled in the art would appreciate that a similar problem could occur under any conditions where a large change in supply heat is applied to the chiller.
In the prior art, some fixed ramp over time is utilized to control the amount of heat delivered into the chiller system. This is not as efficient as would be desirable, as a fixed ramp does not change with the current system conditions.
When driving the system with exhaust heat from a co-generation application, the rate of heat flow should be regulated by the response of the chiller. There is a maximum temperature rise rate for the chiller that is a function of its capacity and design. If too much heat is being applied to the chiller it will exceed this rate and will have the undesirable effects described above. Conversely, if the chiller is heated at a very slow rate, the chiller will not be able to get up to full operating capacity in a reasonable amount of time.
This invention is the control approach which is used to quickly bring the chiller up to full capacity while managing the temperature rises in the solutions to preventing the undesirable effects of uncontrolled rapid heat-up rates